In the method of optical parameters (e.g., absorption), there is the problem that the measured variable cannot readily be determined as an absolute number. It is therefore often necessary to use a second optical signal (reference radiation) of a different wavelength for standardization in addition to the electromagnetic radiation (signal radiation) used for the actual measurement. It is especially desirable for these (two) signals to have a precisely defined intensity ratio.
In the prior art it is known that the two signals may be generated by two individual separate semiconductor components (e.g., by two laser diodes). However, there is the problem here that the two signals must be combined by complex optical systems.